A federal appeals court will hear arguments Tuesday in a case challenging the NSA's vast phone data collection program the next act in the legal battle pitting the agency's antiterrorism efforts against the privacy rights of Americans.

Privacy advocates head into the arguments with a lower court victory in hand: A judge in Washington ruled in their favor in December, calling the technology to gather and analyze the phone records "almost Orwellian."

The lawsuit brought by conservative activist Larry Klayman is one of several filed after former NSA contractor Edward Snowden revealed the data collection program a leak that has opened the way for judges to scrutinize the agency's surveillance activities, and could propel the issue to the Supreme Court.

"Whatever one thinks of Snowden, we're only here because of him," said Stephen I. Vladeck, a law professor at American University.

The National Security Agency, which is headquartered at Fort Meade, says it mines "telephony metadata" the times of calls, numbers dialed and the duration of conversations in search of links between people making calls in the United States and suspected terrorists.

The government says the technique respects Americans' constitutional right to privacy because the records already have been handed over to phone companies, and they do not include the contents of the conversations.

The American Civil Liberties Union and the Electronic Frontier Foundation have filed briefs in support of Klayman. Klayman said the NSA's "unconstitional acts affect all segments of society."

"This case is unique in that both conservatives and liberals alike have joined to represent the American people," Klayman said in a statement.

The NSA referred questions about the case to the Justice Department. The Justice Department did not respond to a request for comment.

U.S. law enforcement, police and spies alike have raced to find ways to use information shed by criminals and terrorists as they move through the digital world.

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Appeals court to weigh NSA phone data program